This invention relates to monitoring systems for monitoring transition of conductive states of superconductive coils, and more particularly to monitoring systems for quickly detecting conductive transition from superconductivity to normal conductivity of superconductive coils excited by AC power supplies.
Recently, many types of superconductive coils excited by low AC loss have been developed. Superconductive coils of the AC excited type are almost in the stage of practical use. Even in this type of superconductive coils, as in the case of the DC excited superconductive coils, when the quench occurs in the superconductive coil, an appropriate measure must be taken quickly. As well known in this field, the quench means a conductive state transition of the superconductive coil from superconductivity to normal conductivity. This appropriate measure can be accomplished by quickly detecting the occurrence of quench. In the case of the AC excited superconductive coil, a constantly varying voltage appears across the coil. Because of this fact, a quench detecting method similar to that of the DC excited superconductive coil cannot be applied to the AC excited superconductive coil for quench detection purposes. For this reason, there is strong demands for the development of some means of quickly detecting the quench of the superconductive coil under its AC excitation.